Social attention is the process of perceiving visual features, such as motion patterns, that specify other people, their distinct characteristics, and their social group memberships, and it is vital to our ability to observe, understand, and participate in social interactions. The proposed experiments will provide the first comprehensive examination of infants' social attention and categorization by describing conditions under which 3- to 12-month-old infants categorize point-light displays produced from recordings of adults from different social groups. This is a formative time in perceptual and cognitive development, and it is characterized by rapid developmental change in perception and learning of environmental structure, including social information. This research will bring new findings and new theoretical perspectives to longstanding debates about the origins of social knowledge and social learning that stem from typical developmental trajectories of visual attention to social stimuli. The short-term objectives of the proposed research are to discover how developing perceptual and cognitive skills yield discrimination, categorization, identification, and learning f biological motion in infancy. The long- term goals are to clarify theories of social categorization and social development and to contribute to characterization of developmental disorders such as autism spectrum disorder, for which there may be specific deficits in social attention. Such an understanding may lead to assessment tools more closely tailored to early diagnosis and treatment than are presently available.